Funding for this research was provided by:
National Natural Science Foundation of China (81973606, 81902247)
Received: 22 March 2020
Accepted: 24 June 2020
First Online: 1 July 2020
Ethics approval and consent to participate
: CHARLS study is an open dataset, informed consent from IRB is not required.
: Not applicable.
: The authors declare that they have no competing interests.